Refugees fleeing war-torn Yemen have arrived by boat in almost equally violent Somalia, the United Nations said on Wednesday in a surprising reversal of a decades old trend which saw Somalis escaping to Yemen.

The UN refugee agency UNHCR said the "first groups of Yemenis fleeing conflict" have arrived on Somalia's northern coastline after crossing the dangerous seas of the Gulf of Aden and landing in the semi-autonomous regions of Somaliland and Puntland.

UNHCR in Somalia said it was "standing by" for more arrivals after the first 32 refugees arrived at the port of Berbera in Somaliland on Saturday.

The refugees braved a 12 hour sea crossing after fleeing the Yemeni city of Taez which was seized by Shiite Houthi rebels last month and targeted by Saudi-led coalition airstrikes in recent days.

The group, including the "elderly and children", are the first recorded to have sought refuge in Somalia while other Yemeni refugees are reported to have arrived in neighbouring Djibouti.

A sea channel only 30 kilometres (20 miles) wide at its narrowest point separates Djibouti and Yemen.

Aid groups fear that a major humanitarian crisis is brewing in Yemen. UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein has warned that Yemen "seems to be on the verge of total collapse".

The movement of refugees from Yemen to Somalia reverses a decades-old trend whereby Somalis have sought safety in Yemen. Even as Yemenis begin to arrive in Somalia the Arabian peninsula nation continues to host more than 238,000 Somali refugees, according to UNHCR.

Somalia's northern regions are impoverished and have suffered the knock-on effects of years of outright civil war further south, but are largely peaceful. In the southern parts of the Horn of Africa nation, African Union and Somali troops continue to battle Al-Qaeda-linked Shebab insurgents.